The invention relates to a supply unit for fluids. Supply units for fluids, such as the roller cell pumps which are frequently used for supplying fuel under pressure, are known in a variety of types. As in FIG. 1, which shows the known prior art illustrated in schematic fashion, such pumps include a rotor disc or grooved disc 1 having reception grooves 2 distributed about its circumference in which are located positive-displacement bodies 3. These bodies 3 may be formed as rollers, which are guided and slide in the grooves 2 and which contact an external roller path 4; the path 4 is of circular shape like the circumference of the grooved disc 1 but is, however, eccentrically shifted by a certain given distance at its center, so that crescent-shaped pumping work chambers are created which travel about the circumference of the system and supply the induced fluid, such as fuel, to an external groove 13 and, via the play between the roller and reception element to an internal pressure groove 10 while the fluid to be supplied or the rotor disc 1 rotates along the arrow A in its eccentric displacement with respect to roller path 4. Because of the eccentricity, a widest gap WS between the roller path 4 and the jacket surface of the rotor and a narrowest gap ES result, which gaps naturally are periodically traversed by the rollers 3 in their grooves upon the rotation of the driven rotor.
In order to understand the present invention, it is necessary also to explain the functional sequence of a known roller cell pump to a certain extent, with the aid of FIGS. 2a through 2c and FIGS. 3a through 3e and the individual working phases represented thereby in order, thus, to clarify the disadvantages inherent therein.
In FIG. 1, the following references are also given, which appear as well in the working phases of FIGS. 2 and 3. V.sub.1 and V.sub.2 indicate, respectively, the chamber under roller 3.sub.1 and 3.sub.2 ; the crescent-shaped chamber between rollers 3.sub.1 and 3.sub.2 and that between rollers 3.sub.2 and 3.sub.3 are designated V.sub.3 and V.sub.5, respectively. The pressure side, extending in each case from the uppermost roller which has passed with widest gap WS, toward the bottom on the left-hand side of the system shown in FIG. 1, is marked D, and the intake side is marked S.
First, the buildup of pressure at the widest gap WS will be described in various working phases with the aid of FIGS. 2a through 2c; for the sake of simplification, a supply medium free of bubbles, such as fuel, is assumed. In FIG. 2a, the roller 3.sub.1 separates the intake chamber S, in which intake pressure prevails, from the chamber V.sub.1 under the roller 3.sub.1 and from the crescent-shaped chamber V.sub.3 between the rollers 3.sub.1 and 3.sub.2. A buildup of pressure has not yet occurred in chambers V.sub.1 and V.sub.3 ; thus, intake pressure also prevails in chambers V.sub.1 and V.sub.3. The forwardmost edge 8 of the chamber V.sub.1 has not yet reached the overlap area of the protruding chamber portion 9 of the internal pressure groove 10, in which, as in the pressure chamber 11 and the crescent-shaped chamber V.sub.5 located in front of the roller 3.sub.2, operational pressure prevails. The distance of the forward edge 8 from the protruding area 9 of the pressure groove 10 amounts to approximately 10.degree., as shown.
Within the next 3.degree., that is, at a distance of 7.degree. between the two parts 8 and 9, a substantial pressure buildup (compression) results in the closed chamber comprising V.sub.1 and V.sub.3, as a result of the reduction in volume of chamber V.sub.3 (FIG. 2b). Within these 3.degree., a substantial pressure peak of over 10 bar can occur in this chamber V.sub.1 plus V.sub.3, as a result of which, roller 3.sub.2 lifts from its previous contact at the rearward groove edge (as seen in the direction of rotation. As a result, there is a connection of the crescent-shaped chamber V.sub.3 and chamber V.sub.1 with the pressure chamber over the area through which the arrow B extends. The chamber V.sub.1 under the roller 3.sub.1 is, as may be seen, not yet directly connected with the pressure groove 10.
Only in the working phase shown in FIG. 2c are both the crescent-shaped chamber V.sub.3 and the chamber V.sub.1 first connected with the pressure chamber 11 via the pressure groove 10, whereby the fluid, displaced out of the chamber V.sub.3, flows past the rollers 3.sub.1 and 3.sub.2 into the pressure chamber in accordance with arrows B and B'.
The working phases shown in FIGS. 3a through 3e show the pressure conditions and the sealing at the narrowest gap ES with pumping bodies or rollers 3.sub.1, 3.sub.2 and 3.sub.3, in the meantime, having traveled farther in the rotary direction. As may be seen, the intake chamber or intake spheroid 12 extends nearly to the narrowest gap ES and, in the working phase shown in FIG. 3a, is already connected with the chamber located in the area of roller 3.sub.3. At this point, the crescent-shaped chamber V.sub.3 is connected as indicated by arrow C with an external pressure groove 13 whereby the fluid displaced out of the crescent-shaped chamber V.sub.3 flows via the external pressure groove 13 and, according to arrow E, past the roller 3.sub.2 via the inner pressure groove 10 into the pressure chamber 11. The gap width at the narrowest gap ES determines the leakage quantity overflowing out of the crescent-shaped chamber V.sub.5 formed between rollers 3.sub.3 and 3.sub.2 and into the intake chamber. In the crescent-shaped chamber V.sub.5, operational pressure prevails.
In the working phase of FIG. 3b, the connection from chamber V.sub.2 under roller 3.sub.2 via the inner pressure groove 10 to the pressure chamber 11 is interrupted, for the groove bottom area 14 at that point is just leaving the inner pressure groove 10. The fluid displaced out of chamber V.sub.2 and the crescent-shaped chamber V.sub.3, which is becoming narrower and narrower, flows via the external pressure groove 13 according to arrow F into the pressure chamber, whereby chamber V.sub.5 is still connected via the external pressure groove 13 with the pressure chamber and a leakage quantity continues to overflow into the intake chamber area.
Only in the working phase of FIG. 3c is the chamber V.sub.5 first separated by the roller 3.sub.2 from the external pressure groove 13 whereby the pressure in chamber V.sub.5 rapidly drops as a result of the quantity of overflow across the narrowest gap ES. Roller 3.sub.2 is pressed by the operational pressure in chamber V.sub.2 and the crescent-shaped chamber V.sub.3 against the forward groove edge, as shown at reference numeral 15, and thus seals off chambers V.sub.2 and V.sub.3 from chamber V.sub.5. From this moment, the leakage quantity at the narrowest gap is no longer determined by the gap width of distance but rather by the remaining volume of chamber V.sub.5 whereby the fluid, further displaced out of chambers V.sub.2 and V.sub.3, flows via the external pressure groove 13 into the pressure chamber 11. Between groove 13 and chamber 11, there is a connection which is not shown.
In the working phase of the parts in FIG. 3d, the roller 3.sub.2 seals off chambers V.sub.2 and V.sub.3 from the intake chamber at the narrowest gap, because the roller 3.sub.2 continues in contact with the forward groove edge. From this point on, the chamber V.sub.2 under the roller 3.sub.2 becomes larger, because the roller 3.sub.2, with the roller path growing increasingly distant from the rotor, moves farther and farther out of its groove. Simultaneously, the gap 16 between the rear groove edge and the roller path grows smaller and smaller and finally reaches the gap distance established by the narrowest gap ES.
The operational pressure available in chamber V.sub.2 then drops as well, when the quantity flowing from chamber V.sub.3 toward chamber V.sub.2 is smaller than the volumetric increase of chamber V.sub.2 resulting from the further rotation of the rotor.
In the working phase of the parts as shown in FIG. 3e, the rear groove edge is at the narrowest gap ES and the gap between groove edge 17 and roller path has reached the minimum. As seen on the leakage quantity flowing through the narrowest gap ES is smaller than the volumetric enlargement of chamber V.sub.2, the roller 3.sub.2 lifts from the forward groove edge at 18 and the pressure in chamber V.sub.2 drops practically at once to the lesser intake pressure, or below. The difference between the particular groove volume and the roller volume each time a roller traverses the narrowest gap ES is the so-called clearance volume, which is reduced upon traversal of the narrowest gap ES from the operational pressure to the intake pressure.
In such a supply pump for fluids having an eccentric, circular roller path, difficulties arise which may be quite substantial as a result of the lack of sealing at the narrowest gap and as a result of unfavorable expansion and compression relationships after the narrowest gap ES and before the widest radial gap WS, particularly (with respect to a fuel supply pump) during so-called hot-gasoline operation.
Since the sealing point between the pressure chamber D and the intake chamber S is formed only by a jacket line having the desired radial play (ES) of a few .mu.m and, as explained above, the distance between the rotor and the roller path rapidly increases with increasing distance from the narrowest gap ES, a large quantity of fuel can flow back from the pressure side to the intake side and there cause functional interruptions as a result of volatilization, particularly during hot-gasoline operation.
The beginning of the intake spheroid 12 must also not be brought too close to the narrowest gap ES, because otherwise a direct connection could result between the pressure side and the intake side as a result of a shortcut via the roller groove in the rotor disc. However, this has the result that, after the narrowest gap, there is an expansion of the sealed chamber volume which, until the intake spheroid is opened, that is, until the intake spheroid 12 is reached, can cause significant underpressures, so that the return flow of fuel and its volatilization are still further encouraged.
Furthermore, at the closing of the intake spheroid 12 before the widest gap WS (see FIGS. 2a-2c), that is, when a particular roller area leaves the intake spheroid area, a compression phase has already occurred for the external partial chamber volume between the rotor and the roller path, while, in contrast, the inner partial chamber volume in the roller groove enlarges still further, which can also have undesirable effects.
There is accordingly a need for a supply unit for fluids whose basic concept corresponds to a roller cell or vane cell pump and in which the disadvantages of the known eccentric circular roller path which are described above are avoided, that is, in which the sealing effect of the radial gap is increased and the expansion and compression phases are adapted to the opening and closing conditions of the intake and pressure spheroids.